Method of producing magnetic materials



Patented Feb; 26, 1929.

UNITED s'rarss- PATIENT. OFFICE...

' JOHN urmmws, or .cmcaeo, rumors, asslcnon. 'ro wmm nnc'rmo comm, mconromrnn, or xnwxonx, N. in, a oonrona'rron on NEW YORK.

- iun-rnon or raonucme uaomrnc mums.

30 Drawing. Application filed larch 18, 1927, Serial No. 175,947. Renewed July 7, 1988.

This invention relates to methods of producing magnetic materials, and more particularly to methods of producing brittle magnetic alloys for use in electrical signal- '5 ing apparatus, such as cores for loading coils employed in telephone circuits.

The principal object of the invention is the production of a magnetic'material, having a fine crystalline structure, to facilitate its reduction to a very finely divided form, and possessing to a high degree'those physical, electrical and magnetic properties which make it highly desirable in electrical signaling apparatus, especially in coresffor loadin coils for telephone circuits.

e magnetic material produced in accordance with the invention is of particular advantage in the production ofmagnet cores of the so-called dust'type in which a magnetic material is reduced to-very finely divided particles the particles treated to produce an insulating coatingthereon and pressed into rings or cores. One method of utilizing the finely divided magnetic material to produce loading coil cores is described in the copending application, Serial No. 102,729, filed April 17,1926, b J. W. Andrews and R. Gillis. However, t e magnetic material is not limited in its use to the particular insulator disclosed in the foregoing application nor to any particular form of core, but may be put to any use within the scope of the appended claims.

In accordance with one embodiment, the present invention contemplates the production of brittle alloys of nickel andv iron by partially oxidizing the constituent metals while in the molten state and working the metal in the solid state, while'hot, to produce a fine crystalline structure. More specifically, the invention contemplates the production of brittle nickel iron a loys', generally known as permalloy in which the proportions of its constituents are more than 25% nickel and the remainder principally iron, one form which has proven satisfactory having a nickel content which is approx mately 80% of the whole.

In this embodiment the constituents are melted in an uncovered furnace in thepresence of oxygen and an oxidizing substance, the molten material is boiled until it is oxidized, is poured into a mold and allowed to solidify. The solidified material is then rolled while hot until it cools below the temperature 'of recrystallization, which is a indicated by a tendenc to break in the rolls,

when it is given an a ditional pass throughthe rolls to effect an additional reduction in order to produce. a fine crystalline structure;

One method of oxidizing-the metals'constituting the alloy is disclosed in the copending application, Serial No. 101,179, filed April 10, 1926,.by C. P. Beath and H. M. E. Heinicke, but for the sake of completeness it will also be described in detail herein.

The method of producing the brittle, fine grained material in accordance with the-invention consists in placing the required guantities of nickel and iron in an uncovered urnace, preferably electrically heated, adding a calculated quantity of ,oxidized material of the same purity, and heating the material until it is molten. The meltin is done in an uncovered furnace in order t at the material may be oxidized by atmospheric oxygen; Since, if vir in metal is used, it requires considerable time to obtain a melt which is oxidized to the right ,tlegree, oxidized material may be added tofurnish additional oxygen to reduce the time consumed in completing the operation. Iron oxide in the form of iron ore may also be added to furnish oxygen within the bath. When the material has become molten it is oxidized by boiling for a length of time determined by the amount of oxidation desired and the type of furnace used. The degree of oxidation of the material depends upon the length of the melting period, the length of the boilingperiod, the amount of the surface of the melt exposed to the air, and the amount of oxy en resent in the char ed material, and the. eating and boiling periods are governed by the various charges and the type of furnace used. Experiments have shown that the metal of a melt which is not sufiiciently oxidized is not sufliciently brittle. -Gonsequently to insure the exact amount of oxidation, the melt is heavily oxidized and a small quantity of a suitable deoxidizer, such as magnesmm-nickel alloy, aluminum or chromium, may be added just before the melt is poured. After the molten material has been boiled the required length of time,

it-is then poured into an ingot mold, and as soon as the material is solidified, the mold is removed and the ingot is allowed to cool.

Samples of the material are taken from varidus parts of the ingot which am. am

alyzed, and if the material is of the re quired composition it is placed in a furnace where it is heated to approximately 1325 C., at which temperature it may be easily rolled. In order to obtain a fine dust, the material should have a very fine crystalline structure, which is obtained by successively assing the hot billets "from the heating turnace, without a subsequent reheating, through progressively reducing rolls until the material has cooled to a temperature below its temperature of recrystallization, which experiments have shown to be at about the temperature at which the'material becomes cold short, that is, the temperature at which the material breaks very readily when struck. The material is then broken into short, lengths which are fed between rolls placed more closely together than any in the prior series which effect a further reduction in the thickness of the material and at the same time efi'ec-ta further reduction in the crystalline structure of the material.

The working of the metal breaks down the large grained, crystalline structure of the billet and produces a very fine grained crystalline'p'roduct which is extremely brittle. Since the final reduction in the size of the crystal is efiected at a temperature below the temperature of recrystallization of the material, the crystals do not grow in size after the final rolling and the resulting product has an extremely fine crystalline structure which is very desirable because in this material the fracture takes place prin'cipally along the crystalline boundaries and I consequently the finer the grain structure the finer the dust which can be produced from the finished product.

The short pieces obtained b the above operations are crushed in a JZLW crusher", hammer mill, or any other suitable type of apparatus, after which the crushed material is rolled in a ball mill until it is reduced to a fine dust. The dust is sieved through a 120 mesh sieve and any residue is remelted and carried through the above operations to again reduce the material to a finely di vided form.

By using an alloy of the proportions stated in the preceding paragraph and by following the foregoing method of procedure, a very fine grained crystalline prodnot is obtained which is extremely brittle and which when reduced to a fine dust yields a large percentage of particles which are small enough to pass through what is commonly known as a 200 mesh sieve.

When reduced to a finely divided form, the

material is then in a form to be used for either continuous or lump loading of telephone circuits.

. The method of producing a magnetic material having a ver fine crystalline structure is also applicablb for use with magnetic materials which have been rendered brittle by the addition of metallic embrittling agents such as antimony, tin, etc, and which have the property of fracturing principally along the crystal boundaries. It mechanical work, such as rolling, is performed upon such alloys at temperatures slightly below their respective temperatures of recrystallization, the resulting materials will have heated to a high temperature, are individually insulated by treating the particles in such a manner as to produce an, insulating coating around each particle, the insulated material formed into rings or cores. by the application of a high pressure, and the rings annealed to stabilize the insulator and to give the rings the desired magnetic properties. A plurality of rings thus formed are then stacked coaxiall to form a core on which the usual toroi al winding is applied, the number of such rings used depending upon the existing electrical characteristics of the telephone circuit with which the loading coils are to be associated. Since, in order to have low losses in loading coil cores made of permalloy dust in the above described manner, it is desirable that all of the material pass through a 120 mesh sieve and a large percentage pass throughv a 200 mesh sieve, it is readily seen that the material produced according to this invention is especially adapted to be used in the production of such cores.

What is claimed is:

1. The method of preparing magnetic materials which fracture principally along the crystal boundaries thereof, which consists in working the material at a temperature slightly below its temperature of recrystallization to produce a fine crystalline structure, and subsequently reducing the material to a finely divided form.

2. The method of making magnetic matorials, which consists in treating a magnetic material to render it brittle and working the material at a temperature below its temperature of recrystallization to produce a fine crystalline structure.

3. The method of making materials, which consists in treating a nickel-iron alloy with an embrittling agent, and rolling the resulting material after it becomes cold short to effect a change in the crystalline structure.

4. The method of making brittle magnetic materials, which consists in partially magnetic v oxidizing a magnetic material and working the material after it becomes cold short to produce a fine crystall ne structure.

netic materials, which consists in partially oxidizing a magnetic material and working the material at a temperaturebelow the temperature of recrystallization to effect a change in the crystalline structure. I

6. The method of making brittle nickel: iron allo s, which consists in partially oxidizing t e v constituents and working the alloy at a temperature below its tempera ture of recrystallization.

7. The method of making brittle mag netic alloys, which consistsin partially oxidizing a'nickel-iron alloy while in the molten state, allowing the material to solidify while hot until it becomes cold short,

5. The method of making brittle mag and then carrying the material through an additional rolling operation.

9. The method of making brittle magnetic alloys composed of more than nickel and the remainder principally iron,

which consists in melting the ingredients in the presence ofoxygen, boiling the ingredients until oxidized, allowing the resulting alloy to solidify, and rolling the alloy at atemperature ,;,be1ow its temperature of re-' crystallization.

10. The method of preparing, magnetic materials in finely divided form,'which consists in melting approximately 80 parts of nickel and 20 parts of iron in the presence of oxygen, boiling the moltenmaterial until oxidized, allowing the resulting alloy to solidify, rolling the alloy while hot until it has reached a temperature below its temperature of recrystallization, and... subsequently reducing the material to finely divided particles.

In witness whereof, I hereunto subscribe my name this 4th day of March A. D., 1927 JOHN WENDELL ANDREWS. 

